Many of the differentials used in automotive drivelines include a planetary gearset which is supported within a differential casing to facilitate relative rotation (i.e., speed differentiation) between a pair of output shafts. For example, in parallel-axis differentials the gearset typically includes a pair of helical side gears that are splined to the ends of axle shafts and which are meshed with paired sets of helical pinions journalled in gear pockets formed in the differential casing. Since the gear pockets are parallel to the rotary axis of the differential casing, each pinion rotates on an axis that is parallel to the common axis of the axle shafts and the side gears. As is known, the torque transmitted through meshed engagement of the side gears and pinions generates thrust forces that are exerted by the gear components against the wall surface of the gear pockets and other thrust surfaces within the differential casing to frictionally limit speed differentiation and proportion torque between the axle shafts.
To facilitate assembly of the gearset, the differential casing is a two-piece assembly having an elongated drum housing mounted to a cover plate. Typically, the gearset is mounted in an interior chamber formed in the drum housing which is then enclosed by the cover plate. When assembled, a radial mounting flange on the drum housing mates with a rim segment of the cover plate. As is conventional, a ring gear is secured to the drum housing via bolts mounted in aligned bores in the mounting flange and rim segment. One problem associated with conventional helical parallel-axis differentials pertains to maintaining proper alignment between the differential casing and the gearset. This problem frequently occurs with two-piece differential casings when the case components do not properly align such that the axle bores are misaligned relative to one another and with respect to the mounting flange.
To guard against the manufacture of differentials with excessive misalignment between the axes of the various rotary components, some manufacturers have incorporated an assembly step into their manufacturing process wherein the two case components are assembled together and subsequently machined as a unit. While this assembly step has been employed with some degree of success, this process is costly due to the subsequent need to disassemble the casing for the installation of the gearset. Furthermore, precise alignment of the components cannot be guaranteed after disassembly of the two-piece casing and, as such, some degree of misalignment is still unavoidable. Consequently, there remains a need in the art for a helical parallel-axis differential assembly with means to improve the relative alignment between the differential case, the axles, and the gear components of the gearset.